Freescale Semiconductor MCF54455 Reference Manual page 885

Debug Module
The _ command can be used to dynamically access the PC for performance monitoring. The
SYNC PC
execution of this command is considerably less obtrusive to the real-time operation of an application than
a - / - /
HALT CPU READ PC RESUME
Command Formats:
15 14 13
0x0
Command Sequence:
Operand Data: None
Result Data: Command complete status (0xFFFF) is returned when the register write is
complete.
34.4.1.5.10 Force Transfer Acknowledge (
Debug revision D logic implements the new
condition. In some system designs, references to certain unmapped memory addresses may cause the
external bus to hang with no transfer acknowledge generated by any bus responders. The
generation of a transfer acknowledge signal.
There are two scenarios of interest: one caused by a processor access and the other caused by a BDM
access. The following sequences identify the operations needed to break the hung bus condition:
• Bus hang caused by processor or external or internal alternate master:
— Assert the breakpoint input to force a processor core halt.
— If the bus hang was caused by a processor access, send in
processor is halted, as signaled by PST = 0xF. Due to pipeline and store buffer depths, many
memory accesses may be queued up behind the access causing the bus hang. Repeated
_ commands eventually allow processing of all these pending accesses. As soon as the
FORCE TA
processor is halted, the system reaches a quiescent, controllable state.
— If the hang was caused by another master, such as a DMA channel, the processor can halt
immediately. In this case as well, multiple assertions of the
required to terminate the alternate master's errant access.
• Bus hang caused by BDM access:
— It is assumed the processor is already halted at the time of the errant BDM access. To resolve
the hung bus, it is necessary to process four or more
command may have initiated a cache line access that fetches 4 longwords, each needing a
unique transfer acknowledge.
34-43
command sequence.
12 11 10 9
0x0
Figure 34-37.
SYNC
SYNC_PC
???
Figure 34-38.
SYNC
FORCE
8 7 6 5
0x0
_ Command Format
PC
NEXT CMD
CMD COMPLETE
_ Command Sequence
PC
_ )
FORCE TA
_ serial BDM command to resolve a hung bus
TA
FORCE
FORCE
_
FORCE TA
4 3 2 1
0x1
_
FORCE TA
_ commands until the
TA
_ command may be
TA
commands, because the BDM
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0
forces